1. Field of the Invention
The present invention relates to an apparatus and methods for actively controlling the interaction of a stylus pen with a touch-screen containing device.
2. Description of the Related Art
Touch-screen tablet computers allow a user the ability to interact directly with content displayed on the touch-screen of the tablet computer. These interactions can be conducted through various means, but typically are done through touch, by way of the user's fingers directly interacting with the screen, or through the use of a stylus pen or other type of input control device that contacts the screen based on movements made by the user. Touch-screens are generally adapted to recognize a position of the touch event on the touch sensor panel at a desired moment in time, and an attached computing system then uses the collected touch event data to control one or more operations based on the received touch event data. A finger, stylus pen or other interacting object are sensed so that various functions can be performed by the touch-screen tablet computer. Most conventional touch-screens are adapted to interpret the various touches supplied by either a finger, stylus pen or other object, either individually or as a single gesture, in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.
Typically, touch-screens distinguish touch inputs from stylus pen inputs by use of various conventional sensing technologies (e.g., optical pens and optical sensors) or by use of input modes that require the user to select a certain type of input device based on the operations the user wants to conduct on the touch-screen of the tablet computer. Other typical solutions require stylus pen inputs to originate from a stylus pen that is physically tethered to the tablet computer. Physically tethered stylus pens require some electrical and physical integration with touch-screen tablet computer, and are often inconvenient to handle and can easily fail due to wear on the connecting components that tether the stylus pen to the touch-screen tablet computer.
A touch-sensing signal output from a touch-screen can be a composite signal, for example, that includes one or more signals caused by a touch and one or more signals caused by other sources, such as electrical interference, which does not provide information about the touch interaction. These other sources, or error sources, can cause a change in the operation of touch sensing that causes the portion of the touch sensing signal that carries touch information to inaccurately reflect the amount or position of the touch.
FIG. 1 is a schematic view of a portion of a mutual capacitance sensing type touch-screen containing device, generally referred to herein as a host device 100, that is used to sense the position of a conductive input object, such as a finger 115 over a user interface 104 portion (i.e., a touch screen) of the host device 100. The host device 100 generally includes the user interface 104, a driver assembly 113 (which may also be referred to herein as a “column driver”) and sensing assembly 117. A mutual capacitance based touch system can include, for example, drive regions and sense regions, such as drive electrodes 114 and sense electrodes 116. For example, drive electrodes 114a-114c (generally oriented in the x-direction) can be formed in rows while sense electrodes 116a-116b (generally oriented in the y-direction) can be formed in columns. Touch-sensing areas, or touch pixels, can be formed at regions where the drive electrode 114 and the sense electrode 116 overlap or are adjacent to each other. A mutual capacitance CM is formed between the drive electrode 114 and sense electrode 116 at a touch pixel. During operation, the drive electrodes 114 may be stimulated with a waveform by driver assembly 113. Because the value of mutual capacitance CM may be too small to be precisely measured during a small window of time (e.g., during a single scan cycle of user interface 104), the driver assembly 113 may typically send a series of pulses via the mutual capacitance CM, that may be integrated and measured at the sensed capacitance Cs in the sensing assembly 117. As a conductive input object approaches the touch pixel, some of the charge being coupled between the row and column of the touch pixel can instead be coupled onto the conductive input object, thus forming an input object capacitance CF. It is well known in the art that the interaction and coupling of the conductive input object, such as a finger or large stylus pen, will cause a charge accumulated in a sensed capacitance Cs in the sensing assembly 117 to decrease, compared with the charge at a sensed capacitance Cs when no conductive input object interacts with the drive and sensing electrodes of the user interface 104. This reduction in charge coupling across the touch pixel can result in a net decrease in the measured mutual capacitance CM between the drive electrode and the sense electrode and a reduction in the waveform being coupled across the touch pixel. This reduction in the charge-coupled waveform can be detected and measured by analyzing the change in the sensed capacitance Cs in the sensing assembly 117 to determine the positions of multiple objects when they touch the user interface 104. In some embodiments, a user interface 104 can be a touch-screen of any of the following types: multi-touch, single touch, projection scan, full-imaging multi-touch, or any other capacitive touch.
To provide touch sensing capability using a stylus pen, typically a tip of a conventional stylus pen has been sized so that the capacitive sensing components in the touch screen device can sense the tip when it contacts the surface of the touch screen. Thus, the tip of the stylus pen is large enough to interfere with the electric field lines created between the drive and sense electrodes of the touch screen device. As such, conventional styluses are passive input devices in that they are incapable of actively altering the input received by the capacitive sensing components in the touch screen or sensing a touch-induced capacitance change in a capacitive touch sensor panel when it is desired to input touch related information.
Despite the progress made with respect to operating touch-screen tablet computers, there is a need in the art for improved methods and apparatus related to an active stylus pen that is configured to provide input to any type of touch-screen tablet computer in spite of the problems discussed above.